I have implemented GuiXT on some of our supervisors' machines, but one of them is getting a pop up box stating "No values available" each time he does a right hand click. How can this be rectified?

In GuiXT profile there is a group box "History". It contains a checkbox "Show on right mouse button". When you deselect the checkbox and relogon to SAP, the normal right mouse button functionality will work again in all screens. The GuiXT history function can then still be invoked with the middle mouse button (if present) and also with the Windows "value selection" key on the keyboard.